Pulse width modulation (PWM) is a technique used to control an amount of electric power and/or the waveform of electric power that is transmitted to a load. One or more switches between a supply of electric power and the load are closed and opened at a high rate, defined by a switching frequency. Power is transmitted over the brief pulses. The duration or “width” of the pulses is controlled to, in turn, control the amount of power that is transmitted by each pulse. Collectively, controlling the amount of power in each pulse enables control of the overall amount of electric power that is transmitted and/or of the shape of the waveform over which the electric power is transmitted. Typically, switching mode power converters operate with a fixed switching frequency. The value of the fixed switching frequency is often set to be high enough to avoid saturation of inductive elements when the power converter is transmitting power near a full load for which the converter is designed. Such switching frequencies are often inefficient when used to transmit electric power at less than full load.
Some conventional power converters have two distinct switching frequencies, including a full power mode switching frequency and a burst mode switching frequency that is less than the full power mode switching frequency. The full power mode switching frequency is used under normal operating conditions. When a controller detects that the load is substantially less than the full design load (a threshold typically set by the designer), the burst switching mode is used to reduce power losses.
Other conventional approaches alter the switching frequency or disable output from a power converter when an operating temperature exceeds a threshold level temperature.
These and other features of the present embodiments will be understood better by reading the following detailed description, taken together with the figures herein described. The accompanying drawings are not intended to be drawn to scale.